Meiotic recombination is one of the important biological processes, and may be responsible for many human diseases. In humans, meiotic recombination is known to be clustered mostly at certain "recombination sites" known as recombination hotspots. Although recombination hotspots are often found at the same locations in different human individuals, very little is known about their conservation. In the proposed study, a hypothesis that recombination hotspots in the human genome are highly conserved but are subjected to substantial changes which may be responsible for the generation of new sites, and weakening and extinguishing existing sites. To do so, the short arm of chromosome 18 will be used as the subject for the study. In the first step of the project, 9,000 single sperm samples from three human males, 3,000 each, will be subjected to genotype analysis at 4,000 loci of Single Nucleotide Polymorphisms (SNPs) after whole genome amplification (WGA). This will be done by using a high-throughput genotyping approach developed in the P.I.'s laboratory. Completion of this round of analysis will detect and localize the recombination hotspots to ~4.8 kb regions along length of the chromosomal arm. These spots will be further localized to <1 kb regions by genotyping an additional 4,000 SNPs located in the regions containing crossovers. All crossover-containing intervals (n = 500 to 600) will be subjected to the conservation analysis. Recombination rates in all these intervals will be determined in 20 sperm donors from two ethnic groups by analyzing pooled sperm samples using a previously reported method allowing selectively amplification and detection of sequences containing recombination crossovers. The resulting data may be used, for the first time, to systematically examine the conservation of recombination hotspots on a large-scale, which will help understand the dynamics of the genetic structure of the human genome and design disease association studies.